All vulnerabilities
CVE-2026-109740

Firefox: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component

Mozilla FirefoxApplications & CMS
Open in ThreatlineRecord JSON
CVSS
9.6Critical
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.35%Chance of exploitation activity in the next 30 days, higher than 27% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
Published13 Oct 2026Updated 19 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

Description

Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

Text from CVE List

Affected versions 4

  • Firefoxunaffected: 153.5 through 153.*CVE List
  • Firefoxunaffected: 158CVE List
  • Thunderbirdunaffected: 153.5 through 153.*CVE List
  • Thunderbirdunaffected: 158CVE List

References 5